1. Field of the Invention
Exemplary embodiments of the present invention generally relate to an image forming apparatus, and more particularly, to an image forming apparatus that conveys a recording medium by a conveyance mechanism and transfers an image formed on a surface of an image bearing member onto the recording medium in a nip contact area formed between the image bearing member and a transfer member disposed facing the image bearing member.
2. Discussion of the Related Art
Conventionally, image forming apparatuses incorporate a gate member within a sheet conveyance route extending between a pair of registration rollers and a transfer nip, and a contact/separation mechanism alternately bringing into contact and separating two rollers of the pair of registration rollers, for example.
When forming an image, such image forming apparatuses position a recording medium so that the leading edge thereof can contact the gate member while the registration rollers are separated from each other and before the rollers contact each other. Then, the image forming apparatuses deactivate the gate member to forward the recording medium from the pair of registration rollers to the transfer nip at a given timing. This configuration can minimize the chances of the leading edge of the recording medium from being bent even when the recording medium is being curled.
Further, some known image forming apparatuses include a timing roller disposed downstream from the gate member in a direction of conveyance of the recording medium conveyed by the gate member. After forwarding the recording medium, the pair of registration rollers may be separated from each other again just as the leading edge of the recording medium reaches the timing roller. With image forming apparatuses having this configuration, after the trailing edge of the recording medium has passed the gate member, a subsequent recording medium may contact the gate member expeditiously so as to be ready for a next image forming operation, thereby effectively enhancing or speeding up sequential printing by reducing operating time thereof.
In one related-art image forming apparatus, at least one conveyance mechanism such as a pair of registration rollers and a timing roller is disposed upstream from the transfer nip in a direction of conveyance of the recording medium. In addition, a conveyance speed of the recording medium is generally controlled to be greater in the conveyance mechanism than in the transfer nip.
With this configuration, when one part of the recording medium is held in the transfer nip and another part in the conveyance mechanism, an area between those parts where different parts of the recording medium are sandwiched may deform and bend gradually but increasingly. Then, when passing a point of conveyance force application or a registration point of the conveyance mechanism, the trailing edge of the recording medium, experiencing maximum deformation, may be suddenly released from the sandwiched part and restored to its original shape. This action can cause significant vibration to the trailing edge of the recording medium and further to the recording medium held in the transfer nip, resulting in poor transferability that may give rise to degradation in image quality.
Further, the conveyance mechanism may cause unevenness in conveyance speed with respect to the recording medium due to eccentricity of its own roller. The conveyance mechanism may send the trailing edge of the recording medium toward the transfer nip while an image is being transferred onto the recording medium. With this action, unevenness in conveyance speed caused by the conveyance mechanisms extends to the recording medium that is passing through the transfer nip. This unevenness in conveyance speed can trigger poor transferability, resulting in degradation in image quality.
Conventionally, such degradation in image quality due to unevenness in conveyance speed caused by eccentricity of the conveyance mechanism has not been regarded as a problem. However, in light of increasing market demands for better imaging quality, it is desirable to remedy any degradation in image quality.